It is demanded in quality management in a production process, waste water treatment, environmental analysis, measurement of a biological sample, and the like that dissolved ions contained in a sample solution is measured.
The dissolved ions in the sample solution can be measured with an analysis apparatus such as an ion chromatograph; however, at least a removal of fine particles in the sample solution by filtering is needed. Further, in the case of a sample solution containing protein or lipid, there is a need to remove these. For example, for measurement of a slight amount of ions (perchlorate ion and the like) in cow milk, removal by adsorption of organic compounds with use of an alumina column or decomposition of organic substances by an ultraviolet light is needed in addition to removal of protein by centrifugation, so that several hours are required for analysis of one sample solution.
Also, in the case in which the dissolved ions to be measured that is contained in the sample solution is trace amount or the like, it is demanded that the dissolved ions to be measured is selectively extracted into an extraction liquid (typically, water) from the sample solution in order to improve the measurement precision.
As a method for pretreatment of such a sample solution, there is a method of extracting dissolved ions to be measured by concentration diffusion using a dialysis membrane (for example, see Non-patent Document 1: Journal of Chromatography A, 919(2001)59-65).
In this method, two flow channels are provided so as to intercalate a diffusion dialysis membrane therebetween, where a sample solution is supplied to one of the channels, and an acceptor solution (typically, water) is supplied to the other one of the channels. The dissolved ions contained in the sample solution are moved by concentration diffusion to the acceptor solution side via the diffusion dialysis membrane.
However, by the above pretreatment method, a long period of time is required for a diffusion when the dissolved analyte ion that is contained in the sample solution is low in concentration, thereby raising a problem of increased period of time for measurement.